Chicken interferon-inducible transmembrane protein 3 restricts influenza viruses and lyssaviruses in vitro.

Interferon-inducible transmembrane protein 3 (IFITM3) is an effector protein of the innate immune system. It confers potent, cell-intrinsic resistance to infection by diverse enveloped viruses both in vitro and in vivo, including influenza viruses, West Nile virus, and dengue virus. IFITM3 prevents cytosolic entry of these viruses by blocking complete virus envelope fusion with cell endosome membranes. Although the IFITM locus, which includes IFITM1, -2, -3, and -5, is present in mammalian species, this locus has not been unambiguously identified or functionally characterized in avian species. Here, we show that the IFITM locus exists in chickens and is syntenic with the IFITM locus in mammals. The chicken IFITM3 protein restricts cell infection by influenza A viruses and lyssaviruses to a similar level as its human orthologue. Furthermore, we show that chicken IFITM3 is functional in chicken cells and that knockdown of constitutive expression in chicken fibroblasts results in enhanced infection by influenza A virus. Chicken IFITM2 and -3 are constitutively expressed in all tissues examined, whereas IFITM1 is only expressed in the bursa of Fabricius, gastrointestinal tract, cecal tonsil, and trachea. Despite being highly divergent at the amino acid level, IFITM3 proteins of birds and mammals can restrict replication of viruses that are able to infect different host species, suggesting IFITM proteins may provide a crucial barrier for zoonotic infections.

Identification, cloning and characterisation of interleukin-1F5 (IL-36RN) in the chicken.

The human IL-1 family contains eleven genes encoded at three separate loci. Nine, including IL-36 receptor antagonist (IL-36RN), also known as IL-1F5, are present at a single locus on chromosome 2, whereas IL-18 and IL-33 lie on chromosomes 11 and 9 respectively. There are currently only three known orthologues in the chicken - IL-1ß, IL-18 and IL-1RN - which are encoded on chromosomes 22, 24 and unplaced, respectively. A novel chicken IL-1 family sequence representing IL-36RN (IL-1F5) was initially identified from an expressed sequence tag (EST) library by its similarity to both chicken IL-1RN and chicken IL-1ß. Following isolation of the cDNA from the liver of an uninfected bird, a number of unique sequence features were identified. The predicted protein has a longer NH(2)-terminus than the human protein; however, as in mammals, this region contains neither a prodomain nor a signal peptide. A putative nuclear export sequence is also apparent, yet a similar motif is absent in mammalian IL-36RN. Although chIL-36RN exhibits low homology with its mammalian orthologues, it encodes a predicted ß-trefoil structure whose ß-strands are conserved with those of the mouse sequence. Unlike in mammals, chIL-36RN expression was constitutive in all tissues and cell subsets examined. In response to viral infection, expression was significantly downregulated in a line of birds which are susceptible to the virus. Chicken IL-36RN, like chIL-1RN, is not encoded at the chIL-1ß locus, further emphasising the genomic fragmentation of the large IL-1 gene cluster found in mammals. This suggests differential evolution of this cytokine family since the divergence of birds and mammals from a common ancestor, and underlines the difficulty of determining the full repertoire of chIL-1 family members.